Suspension Feeling Loose After Wider Tires?

[Vapour Trails]

They stick good on hard launches and cornering but the rear end just has more roll.

By roll you mean slide, right?

I guess if they don't improve after more air and the 300 miles I'm about to put on it this weekend then I'll take them back in and order crap OEM Pirellis to replace them.

More air will increase the tendency for the rear end to slide or oversteer. Brand new tires are well-known for being slippery, just do a google search. I'm afraid getting a different brand will end up with the same result. Just take it easy until they are broken in.

 

[DON SVO]

I ran a 305 DR for quite some time, had to get some 285s for a while since I had a cut in one DR and they were about toast anyways. I've never noticed the loose feeling, then again I lowered my car and added LCRs/panhard rod out back at the same time.

 

[JDos1]

By roll you mean slide, right?



More air will increase the tendency for the rear end to slide or oversteer. Brand new tires are well-known for being slippery, just do a google search. I'm afraid getting a different brand will end up with the same result. Just take it easy until they are broken in.

No not slide. Feels like theres more body roll in the rear, as if the sway bar is disconnected.

Maybe that's what you mean by slide.....When I think of slide I think of drifting....

 

[assasinator]

I had stock 255 brembo tires all around.

One weekend I installed Koni Sports shock/struts and some springs... car felt perfect... very close to stock.

The next weekend I replaced the rear tires with 275 Hankook V12s and immediately the rear of the car felt too sensitive.... like on freeway I would wiggle wheel back and froth, the front of the car would respond just find and felt really controlled... rear of the car however felt like it wanted to go all over. It did fell like it could be unsafe, I didn't get how the tires had made this much of a difference to the feel of car.

I then tried turning the rear struts another 1/2 turn towards firm and bam, car felt perfect again. I was really surprised at how much of a difference both these changes were able to make. I was also pretty happy I had got the adjustable shocks.

mine felt that way till i put new tires all around. the p-zero tires are far superior. change the fronts and it will feel better. it will still feel looser, just not dangerous. the issue i have with firming the rear to feel the same is, the higher rear rate will make the car looser if it does break loose. the fronts will hold.

 

[JDos1]

Discount Tire filled them to the Ford recommended 32psi. I checked the sidewall and found that the max pressure was 51psi. Pumped them up to 42psi and all of the body roll has disappeared. Evidently wider tires will need more air. They still grip damn well even with that much air pressure. Threw it through some hard curves and aggressive starts today and all is well. Highly recommend the Hankook Ventus V4 ES H105's.

 

[cyclerick]

Check the load rating on the replacement tires versus stock. If the load rating is higher on the new tires then you can run the stock pressure on the door pillar. If it's less then you need more PSI. Check with manufacturer.
I also found stiffening up the rear shocks made a difference. I went from 245/19 to 315/20 and found the lower pressure and stiffer rear shock setting helped. In my case my new tires had a much higher load rating and when I checked with Michelin they told me that the stock pressure of 32 was fine or I could go lower.

 

[JDos1]

Problem has already been solved as posted above. Tires didn't have enough pressure in them causing the sidewall to not firm up as it should.